METHOD OF PRODUCING HIGH PURITY SiOx NANOPARTICLES WITH EXCELLENT VOLATILITY AND APPARATUS FOR PRODUCING THE SAME

ABSTRACT

The present disclosure provides a method of producing high purity SiOx nanoparticles with excellent volatility and an apparatus for producing the same, which enables mass production of SiOx nanoparticles by melting silicon through induction heating and injecting gas to a surface of the molten silicon. The apparatus includes a vacuum chamber, a graphite crucible into which raw silicon is charged, the graphite crucible being mounted inside the vacuum chamber, an induction melting part which forms molten silicon by induction heating of the silicon material received in the graphite crucible, a gas injector which injects a gas into the graphite crucible to be brought into direct contact with a surface of the molten silicon, and a collector disposed above the graphite crucible and collecting SiOx vapor produced by reaction between the molten silicon and the injected gas.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.A. §119 of KoreanPatent Application No. 10-2011-0030414, filed on Apr. 1, 2011 in theKorean Intellectual Property Office, the entirety of which isincorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a technique for producing high puritySiOx nanoparticles and, more particularly, to a method of producing highpurity SiOx nanoparticles with excellent volatility and an apparatus forproducing the same, which enables mass production of SiOx nanoparticlesby melting a silicon raw material through induction heating andinjecting gas to a surface of the molten silicon.

2. Description of the Related Art

Generally, a carbon electrode is used as an anode for lithium ionbatteries. Carbon electrodes are advantageous in terms of high chargeand discharge efficiency. However, the carbon electrode has limitationin application to an anode for next generation lithium ion batteries onaccount of a low theoretical capacity of 375 mAh/g.

Although silicon Si used as an anode material for lithium ion batterieshas a high theoretical capacity of about 4200 mAh/g, Li_(4.4)Si isformed by reaction between Li_(4.4) and Si during charging of thelithium ion battery, thereby causing high volume expansion up to about400%. Such high volume expansion induces cracking or short circuit ofthe anode of the lithium ion battery made of silicon.

On the other hand, although silicon Si is known as undergoing reductionin stress caused by volume expansion when the particle size of siliconvaries from a micrometer scale (μm) to a nanoscale (nm), nanoscalesilicon particles also provide a problem of cracking or short circuit ofthe anode due to volume expansion.

BRIEF SUMMARY

One aspect of the present invention is to provide an apparatus forproducing SiOx nanoparticles, which melts raw silicon by electromagneticinduction heating using an induction coil and injects various gases ontoa surface of molten silicon, thereby enabling mass production of SiOxnanoparticles.

Another aspect of the present invention provides is to provide a methodof producing SiOx nanoparticles using the apparatus.

In accordance with one aspect of the present invention, an apparatus forproducing SiOx nanoparticles includes a vacuum chamber; a graphitecrucible into which raw silicon is charged, the graphite crucible beingmounted inside the vacuum chamber; an induction melting part which formsmolten silicon by induction heating of the silicon material received inthe graphite crucible; a gas injector which injects a gas into thegraphite crucible to be brought into direct contact with a surface ofthe molten silicon; and a collector disposed above the graphite crucibleand collecting SiOx vapor produced by reaction between the moltensilicon and the injected gas.

In accordance with another aspect of the present invention, a method ofproducing SiOx nanoparticles includes: charging raw silicon into agraphite crucible; performing induction heating of the raw silicon inthe graphite crucible to form molten silicon; injecting a gas into thegraphite crucible such that the gas is brought into direct contact witha surface of the molten silicon; and collecting SiOx particles bycooling and condensing SiOx vapor produced by reaction between themolten silicon and the injected gas.

According to embodiments of the invention, the apparatus may producehigh purity SiOx nanoparticles having a particle size of about 50 nm orless at low cost in a short time through application of bothelectromagnetic induction melting and rapid cooling.

In addition, since the SiOx nanoparticles produced by the methodaccording to embodiments of the invention have a high battery capacityof about 1500 mAh/g and may have a particle size of about 50 nm or less,it is expected that the SiOx nanoparticles will increase charge anddischarge efficiency to three times or more that of carbon electrodes.

Further, when the SiOx nanoparticles produced by the method according tothe embodiments are applied to an anode material for lithium ionbatteries, the anode does not suffer from volume expansion and is thusprevented from cracking or short circuit.

Further, when the SiOx nanoparticles produced by the method according tothe embodiments are subjected to carbon coating simultaneously withmanufacture of SiOx particles, application of the carbon coated SiOx-Cparticles to an anode material for lithium ion batteries may improvecharge and discharge efficiency of the lithium ion batteries based onimprovement in electrical conductivity by carbon coating.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the inventionwill become apparent from the detailed description of the followingembodiments in conjunction with the accompanying drawings:

FIG. 1 is a sectional view of an apparatus for producing SiOxnanoparticles according to one exemplary embodiment of the invention;

FIG. 2 is a perspective view of a graphite crucible of FIG. 1;

FIG. 3 is an enlarged sectional view of Part A of FIG. 1;

FIG. 4 is a flowchart of a method of producing SiOx nanoparticlesaccording to one exemplary embodiment of the invention;

FIG. 5 is a picture of SiOx nanoparticles produced by one example; and

FIG. 6 is a scanning electron micrograph of the SiOx nanoparticles ofFIG. 5.

DETAILED DESCRIPTION

Exemplary embodiments of the invention will now be described in detailwith reference to the accompanying drawings. It should be understoodthat the present invention is not limited to the following embodimentsand may be embodied in different ways, and that the embodiments aregiven to provide complete disclosure of the invention and to providethorough understanding of the invention to those skilled in the art. Thescope of the invention is limited only by the accompanying claims andequivalents thereof. Like components will be denoted by like referencenumerals throughout the specification.

A method of producing high purity SiOx nanoparticles with excellentvolatility and an apparatus for producing the same according toexemplary embodiments of the invention will be described with referenceto the accompanying drawings.

FIG. 1 is a sectional view of an apparatus for producing SiOxnanoparticles according to one exemplary embodiment of the invention.

Referring to FIG. 1, the SiOx nanoparticles manufacturing apparatus 100includes a vacuum chamber 110, a graphite crucible 120, an inductionmelting part 140, a gas injector 160, and a collector 180.

Vacuum Chamber

The vacuum chamber 110 provides a closed space for producing SiOxnanoparticles. It is desirable that the vacuum chamber 110 have a cleaninterior kept under vacuum.

Graphite Crucible

The graphite crucible 120 is mounted inside the vacuum chamber 110. Thegraphite crucible 120 is open at an upper side thereof and raw siliconfor SiOx nanoparticles is charged into the graphite crucible 120 throughthe upper side thereof.

FIG. 2 is a perspective view of the graphite crucible of FIG. 1.

Referring to FIG. 2, the graphite crucible 120 has a cylindricalstructure open at the upper side thereof and is provided with aplurality of slits 122, which is formed by cutting part of a wall of thegraphite crucible. The graphite crucible 120 is divided into segments124 by the plurality of slits 122.

In this case, the raw silicon charged into the graphite crucible 120 maybe subjected to direct melting by electronic induction heating throughthe induction melting part 140 (see FIG. 1) described below or subjectedto indirect melting by the graphite crucible 120 which is subjected toinduction heating through the induction melting part.

Induction Melting Part

Referring again to FIG. 1, the induction melting part 140 may include arefractory crucible 142 and an induction coil 144. The refractorycrucible 142 may be configured to enclose the graphite crucible 120. Theinduction coil 144 is wound around an outer periphery of the graphitecrucible 120.

Alternatively, the induction coil 144 may be embedded in a wall of therefractory crucible 142. Although not shown in the drawings, theinduction coil 144 may be attached to an inner wall of the refractorycrucible 142.

The induction melting part 140 melts the raw silicon received in thegraphite crucible 120 through induction heating, thereby forming moltensilicon 130.

The induction melting part 140 generates an electromagnetic fielddirected towards an inner center of the graphite crucible 120. Theelectromagnetic field generated by induction heating causes the moltensilicon 130 to be separated from a sidewall of the graphite crucible 120and to rise up at the center of the graphite crucible 120. In this way,the molten silicon 130 is stirred by the electromagnetic field, therebyincreasing the surface area of the molten silicon 130.

AC current applied to the induction coil 144 of the induction meltingpart 140 may have a frequency of 10 kHz or less. If the frequency of theAC current applied to the induction coil 144 is lowered to 10 kHz orless, the electromagnetic field may be imparted to a deep portion insidethe molten silicon 130, thereby maximizing the flow of the moltensilicon. Such flow of the molten silicon maintains the surface of themolten silicon 130 in a more unstable state, thereby improvingefficiency of volatilizing the molten silicon 130.

Since silicon has low electrical conductivity up to about 700° C., theraw silicon is initially subjected to indirect heating by heat appliedto the graphite crucible 120. Then, when heated to a temperature of 700°C. or more, the silicon rapidly increases in electrical conductivity,thereby allowing electromagnetic induction melting.

In order to produce metallic or non-metallic nanoparticles, various rawmetallic or non-metallic materials may be charged into the crucible forelectromagnetic induction melting. Examples of raw metal materialsinclude, but are not limited to, Si, Ti, Ag, Al, Au, Cu, Pt, Mg, Zn, Sn,and the like to produce the metallic nanoparticles. Further, various rawnon-metallic materials may be used to produce the non-metallicnanoparticles.

Gas Injector

The gas injector 160 injects gas into the graphite crucible 120 to bebrought into direct contact with the surface of the molten silicon.

The gas injector 160 includes a gas supply tube 162 to which gas issupplied from the outside, and an injection nozzle 164 coupled to oneend of the gas supply tube 162 and disposed inside the graphite crucible120. Although not shown in the drawings, the gas injector 160 mayfurther include a gas tank (not shown) disposed outside the vacuumchamber 110 to supply gas to the gas supply tube 162.

Here, an injection gas from the gas injector 160, specifically, from theinjection nozzle 164 of the gas injector 160, generates SiOx vapor 132through reaction with the molten silicon 130, and the SiOx vapor 132flows into the collector 180 disposed above the graphite crucible 120.The injection gas may be injected immediately before the raw siliconmelted by injection heating of the induction melting part 140 forms themolten silicon 130.

Examples of the injection gas may include Ar, H₂, O₂, H₂O, and the like.These gases may be used alone or as a mixture of two or more thereof.Among these injection gases, Ar is mixed for the purpose of dilution andH₂ is mixed for the purpose of reduction. Further, N₂ gas may be mixedto produce nitride-based metal nanoparticles.

The value of “x” in SiOx may be determined according to a partialpressure of the injection gas injected through the gas injector 160.Further, a particle size and shape of the SiOx nanoparticles may bedetermined according to a flux of the injection gas, and the shape andposition of the gas supply tube 162.

Collector

The collector 180 is disposed above the graphite crucible 120 andcollects the SiOx vapor 132 produced by reaction between the moltensilicon 130 and the injection gas.

The SiOx vapor 132 flowing into the collector 180 is subjected tocooling and condensation, thereby producing SiOx particles 134.

The collector 180 may include a gas phase flow section 182, a collectingsection 186, and a gas circulation section 188.

The gas phase flow section 182 is disposed above the graphite crucible120 to face the graphite crucible 120. As a result, the SiOx vapor 132produced by induction melting within the graphite crucible 120 flowsinto the gas phase flow section 182.

The collecting section 186 collects the SiOx particles 134 producedthrough cooling and condensation of the SiOx vapor 132 having passedthrough the gas phase flow section 182. When the SiOx vapor 132 flowsinto the collecting section 186, some of the SiOx vapor 132 is cooledand condensed to produce the SiOx particles 134, and the other flowsinto the gas circulation section 188 described below.

The collecting section 186 may be provided with a certain structure (notshown) which exhibits a sharp temperature difference in order tofacilitate cooling and condensation. Here, the SiOx vapor 132 istransferred by pressure difference created by adjusting pressures of thegas phase flow section 182 and the collecting section 186 to bedifferent from each other.

The gas circulation section 188 circulates the SiOx vapor 132 to allowthe SiOx vapor 132, which is not cooled and condensed, to return fromthe collecting section 186 to the gas phase flow section 182. For thispurpose, the gas circulation section 188 may be provided with acirculation pump 181 for circulating the SiOx vapor 132.

On the other hand, the collector 180 may further include a coating gasinjection section 184 between the gas phase flow section 182 and thecollecting section 186.

The coating gas injection section 184 is provided to perform carboncoating with respect to the SiOx particles 132, which are cooled whileflowing into the collecting section 186 through the gas phase flowsection 182, and may be eliminated as needed. Although not shown in thedrawings, the coating gas injection section 184 may be provided with acoating gas jet nozzle (not shown) through which a coating gas isejected.

Examples of the coating gas include alkane-based gases, such as CH₄,C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄ and the like, in addition to Ar or H₂.These gases may be used alone or as a mixture of two or more thereof.Among these injection gases, Ar is mixed for the purpose of dilution andH₂ is mixed for the purpose of reduction.

The SiOx particles 134 may react with the coating gas, thereby producingSiOx-C particles. In this case, carbon coating may be performedsimultaneously with production of the SiOx particles 134.

Therefore, the apparatus according to this embodiment is capable ofrapidly producing high purity SiOx nanoparticles having a particle sizeof about 50 nm or less at low cost through application of bothelectromagnetic induction melting and rapid cooling.

For this purpose, the apparatus according to this embodiment melts rawsilicon by induction heating through electromagnetic induction using aninduction coil and injects various gases onto a surface of the moltensilicon, thereby enabling mass production of SiOx nanoparticles.

In the apparatus according to this embodiment, the graphite cruciblehaving a plurality of slits is used to melt raw silicon therein throughinduction heating to maximize the surface area of the molten silicon forincreasing volatilization efficiency.

Further, AC current is supplied to the induction coil at a frequency of10 kHz or less to maintain the surface of the molten silicon in anunstable state by maximizing the flow of the molten silicon, therebyenhancing efficiency of volatizing the molten silicon.

Further, the apparatus according to this embodiment allows carboncoating to be performed simultaneously with production of SiOxparticles. When the carbon coated SiOx-C particles are used as an anodematerial for a lithium ion battery, it is possible to achieve furtherimprovement of charge and discharge efficiency of the lithium ionbattery through improvement in electrical conductivity by carboncoating.

FIG. 4 is a flowchart of a method of producing SiOx nanoparticlesaccording to one exemplary embodiment of the invention.

Referring to FIG. 4, the SiOx nanoparticle production method includes asilicon charging operation S210, induction melting operation S220, gasinjection operation S230, and collecting operation S240.

Silicon Charging

In the silicon charging operation S210, raw silicon is charged into agraphite crucible. The graphite crucible is mounted inside a vacuumchamber. The graphite crucible is open at an upper side thereof and maybe divided into segments by a plurality of slits, which are formed bycutting part of a wall of the graphite crucible.

Induction Melting

In the induction melting operation S220, the raw silicon received in thegraphite crucible is subjected to induction heating, thereby formingmolten silicon.

Here, the electromagnetic field generated by induction heating causesthe molten silicon to be separated from a sidewall of the graphitecrucible and to rise up at the center of the graphite crucible. In thisway, the molten silicon is stirred by the electromagnetic field, therebyincreasing the surface area of the molten silicon.

Here, AC current applied to an induction coil surrounding the outerperiphery of the graphite crucible may have a frequency of 10 kHz orless.

If the AC current applied to the induction coil is lowered to 10 kHz orless, the electromagnetic field may be imparted to a deep portion insidethe molten silicon, thereby maximizing the flow of the molten silicon.Such flow of the molten silicon maintains the surface of the moltensilicon in a more unstable state, thereby improving efficiency ofvolatilizing the molten silicon.

Gas Injecting

In the gas injection operation S230, a gas is injected to be broughtinto direct contact with the surface of the molten silicon.

Here, the injected gas generates SiOx vapor through reaction with themolten silicon, and the SiOx vapor flows into a collector. The gas maybe injected immediately before the raw silicon melted by injectionheating forms the molten silicon.

Examples of the injection gas may include Ar, H₂, O₂, H₂O, and the like.These gases may be used alone or as a mixture of two or more thereof Inthe gas injection operation, the value of “x” in SiOx may be determinedaccording to a partial pressure of the injection gas. Further, aparticle size and shape of the SiOx nanoparticles may be determinedaccording to a flux of the injection gas, and the shape and position ofthe gas supply tube 162.

Collecting

In the collecting operation S240, SiOx particles are collected bycooling and condensing the SiOx vapor produced by reaction between themolten silicon and the injection gas.

Although not shown in the drawings, the method may further includeinjecting a coating gas to the SiOx particles to coat the SiOx particleswith carbon during the collecting operation S240.

Examples of the coating gas include alkane-based gases such as CH₄,C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄ and the like, in addition to Ar or H₂.These gases may be used alone or as a mixture of two or more thereof

In this way, the SiOx nanoparticles production method according to thisembodiment may be finished.

Since the SiOx nanoparticles produced by the method according to theembodiment have a high battery capacity of about 1500 mAh/g and aparticle size of about 50 nm or less, the SiOx nanoparticles mayincrease charge and discharge efficiency to three times or more that ofcarbon electrodes.

Further, when the SiOx nanoparticles produced by the method according tothe embodiment are applied to an anode material for lithium ionbatteries, the anode does not suffer from volume expansion and can thusbe prevented from cracking or short circuit.

Example

Next, the constitution and functions of the invention will be explainedin more detail with reference to the following example. The example isprovided for illustrative purposes only and is not to be in any wayconstrued as limiting the invention.

A description of details apparent to those skilled in the art will beomitted.

1. Preparation of SiOx nanoparticles

First, raw silicon is charged into a crucible. The crucible has an outerdiameter of 90 mm, an inner diameter of 60 mm, and a height of 150 mm,and includes 12 slits separated at an interval of 1 mm at 15 degreesfrom each other.

An induction coil having a diameter of 8 mm was turned 10 times aroundthe crucible from an upper portion of the crucible, and AC current wasapplied at a frequency of 6.7 kHz to the crucible through the inductioncoil.

With 250 g of raw silicon charged into the crucible, a vacuum chamberwas kept at a vacuum of 5˜10 Torr for 1 hour or more and Ar gas wasejected into the chamber to provide an operation vacuum of about 2 Torr.

Applied electric power for melting the raw silicon was in the range of1˜20 kW and was gradually increased by 2 kW every 5 minutes for 50˜60minutes. At an electric power of 16 kW, the raw silicon started meltingfrom the center thereof and molten silicon completely melted the chargedraw silicon material while moving from the center of the crucibletowards an outer wall thereof.

Immediately after formation of the molten silicon, 0.1˜5 vol % of amixture gas of O₂ and Ar was injected towards the surface of the moltensilicon to generate SiOx vapor.

It was observed that the SiOx vapor flowed towards a collector disposedabove the crucible, and it could be ascertained that yellow particleswere accumulated near an inlet of the collector into which the SiOxvapor flowed.

The SiOx vapor was converted into SiOx particles in the collectorthrough cooling and condensation. Here, a reaction gas was injected intoa gas circulation section in order to improve yield. In this manner, theSiOx particles were produced through cooling and condensation andcollected by a mesh.

As the raw silicon was completely melted, the molten silicon wasseparated from the sidewall of the crucible and was raised up at thecenter of the crucible. In this way, it could be ascertained that themolten silicon was stirred and increased in the surface area by theelectromagnetic field. Further, it could be ascertained that thevaporized amount was increased with increasing surface area of themolten silicon.

SiOx nanoparticles were produced by injecting an injection gas for 1hour after completely melting the raw silicon and the electric power wasgradually decreased after production of the SiOx nanoparticles tosolidify the molten silicon within the crucible. After opening thechamber, the collected SiOx nanoparticles were separated from a mesh.

2. Property evaluation of SiOx nanoparticles

FIG. 5 is a picture of the SiOx nanoparticles produced by the exampleand FIG. 6 is a scanning electron micrograph of the SiOx nanoparticlesof FIG. 5.

As shown in FIGS. 5 and 6, the produced SiOx nanoparticles had a darkyellow color, and it can be seen that the nanoparticles are uniformlydistributed. In this example, the SiOx nanoparticles have a particlediameter of 10˜50 nm.

As such, the apparatus according to the embodiment may produce highpurity SiOx nanoparticles having a particle size of about 50 nm or lessat low cost in a short time through application of both electromagneticinduction melting and rapid cooling.

Further, since the SiOx nanoparticles produced by the apparatusaccording to the embodiment have a high battery capacity of about 1500mAh/g and a particle size of about 50 nm or less, it is expected thatthe SiOx nanoparticles will increase charge and discharge efficiency tothree times or more that of carbon electrodes.

Although some embodiments have been described herein, it should beunderstood by those skilled in the art that these embodiments are givenby way of illustration only, and that various modifications, variations,and alterations can be made without departing from the spirit and scopeof the invention. Therefore, the scope of the invention should belimited only by the accompanying claims and equivalents thereof.

1. An apparatus for producing SiOx nanoparticles comprising: a vacuumchamber; a graphite crucible into which raw silicon is charged, thegraphite crucible being mounted inside the vacuum chamber; an inductionmelting part which forms molten silicon by induction heating of thesilicon material received in the graphite crucible; a gas injector whichinjects a gas into the graphite crucible to be brought into directcontact with a surface of the molten silicon; and a collector disposedabove the graphite crucible and collecting SiOx vapor produced byreaction between the molten silicon and the injected gas.
 2. Theapparatus of claim 1, wherein the graphite crucible has a cylindricalstructure open at an upper side thereof and is provided with a pluralityof slits formed by cutting part of a wall of the graphite crucible. 3.The apparatus of claim 1, wherein the induction melting part comprises arefractory crucible enclosing the graphite crucible and an inductioncoil wound around an outer periphery of the graphite crucible.
 4. Theapparatus of claim 3, wherein the induction coil is embedded in a wallof the refractory crucible.
 5. The apparatus of claim 3, wherein ACcurrent having a frequency of 10 kHz or less is applied to the inductioncoil.
 6. The apparatus of claim 1, wherein the gas injector comprises agas supply tube to which gas is supplied from outside, and an injectionnozzle coupled to one end of the gas supply tube and disposed inside thegraphite crucible.
 7. The apparatus of claim 1, wherein the injectiongas is selected from Ar, H₂, O₂, H₂O, and a mixture thereof.
 8. Theapparatus of claim 1, wherein the collector further comprises a coatinggas injection nozzle to perform carbon coating of the SiOx particles. 9.A method of producing SiOx nanoparticles, comprising: charging rawsilicon into a graphite crucible; performing induction heating of theraw silicon in the graphite crucible to form molten silicon; injecting agas into the graphite crucible such that the gas is brought into directcontact with a surface of the molten silicon; and collecting SiOxparticles by cooling and condensing SiOx vapor produced by reactionbetween the molten silicon and the injected gas.
 10. The method of claim9, wherein the injection gas is selected from Ar, H₂, O₂, H₂O, and amixture thereof.
 11. The method of claim 9, wherein the inductionheating is performed by applying AC current having a frequency of 10 kHzor less to the induction coil.
 12. The method of claim 9, wherein thecollecting of the SiOx particles comprises ejecting a coating gas ontothe SiOx particles.
 13. The method of claim 12, wherein the coating gasis selected from CH₄, C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄, and a mixturethereof.
 14. SiOx nanoparticles for an anode material of a lithium ionbattery produced by the method according to claim
 9. 15. The SiOxnanoparticles of claim 14, wherein the nanoparticles have a particlesize of 10˜50 nm.